Solid additive-assisted morphology optimization enables efficient nonhalogen solvent-processed polymer solar cells

Controlling and optimizing the photoactive layer morphology is closely related to the process of exciton dissociation, charge transfer and collection and thus is crucial for building a high-performance polymer solar cell (PSC). Due to the limited solubility of non-halogenated solvents and the strong crystallinity of Y6 acceptors, it is a challenge to optimize the morphology of the Y6-based blend active layer processed by a non-halogenated solvent for achieving a high photovoltaic performance. In this work, we develop a morphology controlling method by applying BTBT and DTBDT as solid additives to regulate the phase separation of the o-xylene-processed PM6:Y6 blend films. The strong crystalline behavior of BTBT and DTBDT can restrict the over-aggregation of Y6 molecules in a low volatility processing solvent during the film formation. The stronger crystallinity and better miscibility with Y6 of BTBT over DTBDT lead to a favorable effect in facilitating the formation of a nanoscale bicontinuous interpenetrating network in the PM6:Y6 active layer. As a result, the o-xylene-processed PM6:Y6-based PSC treated with BTBT and DTBDT additives shows an enhanced power-conversion efficiency (PCE) of 16.37% and 14.40%, respectively, as compared to the control device (PCE = 10.25%) using 1-chloronaphthalene as a solvent additive.